Basins are used to collect certain materials and particles from liquid, to clarify the liquid. These materials are initially suspended in the liquid. They are subject to the force of gravity when the flow of the liquid is substantially reduced, as in a very low flow, or quiescent, zone (or flow channel) in the basin, and settle to the bottom of the basin. The settled materials and particles are removed from the bottom of the basin by being drawn into a header conduit that may traverse the bottom of the basin. Since these materials are generally solid and are said to “settle” out of the liquid, they are referred to as “settleable solids”, or “settleable particulates”. Upon settling onto the bottom they are generally referred to as “sludge”. Such settleable solids may include naturally occurring materials (e.g., clay, silts, sand and dirt), chemical precipitants, biological solids, and stringy materials such as fibers. The words “material” or “solids” or “sludge” as used herein to describe the present invention refers to all such settleable solids and settleable particulates.
Basins are used, for example, in water and waste water treatment plants. In water treatment, the water drawn from a water supply has various non-settleable colloidal solids therein. When mixed with chemicals, the colloidal solids and chemicals agglomerate to form solids. In waste water treatment, the solids include organic solids, among other wastes. Water and waste water are treated in basins to remove such solids, thereby making the water clear and suitable for use, reuse, or for further treatment, such as tertiary treatment. The word “liquid” as used herein to describe the present invention refers to water and waste water.
An object of water and waste water basins is to create the quiescent zones having low flow rates to promote maximum settlement of the solids to the bottom of the basins. Typically, basins include a large area for containing the liquid and the solids where the settlement of the solids occurs. Such settlement has been promoted in small area basins by use of plate or tube settlers. Regardless of how the solids are caused to settle from the liquid in the basin, there is a need to remove the settled settleable solids and settleable particulates (i.e., the sludge) from the basin to provide room for additional solids and particulates which settle.
Various devices have been used in basins to remove the sludge from the basin. Among these are the well-known reciprocating sludge collector described in U.S. Pat. No. 4,401,576 which is incorporated herein by reference in its entirety. Other sludge collectors have been mounted to pivot on an axis at the center of a circular basin. Whether the collector reciprocates or rotates on an axis in the basin, a header conduit of the collector is generally caused to move relative to the bottom of the basin into the sludge which collects on the bottom. Negative pressure is applied to one end, or to a central point, of the header conduit in an attempt to cause the liquid and the sludge to flow from the bottom of the basin and enter apertures formed through the wall of the header conduit. The apertures are generally formed by removing a portion of the wall of the header conduit, which is typically a cylindrical pipe or a triangular cross-section conduit made from 14 gauge (75 mil) material. The liquid and the sludge enter the pipe in the direction of a diameter of the pipe, and for sludge removal must eventually turn so as to flow axially in the header conduit toward the downstream point at which the negative pressure is applied to the pipe. Despite some developments in removal of sludge from basins, problems have been experienced in attempting to efficiently remove the sludge from the basin using such header conduits.